Liquid rinse cycle fabric softeners are used to provide a softened feel to garments that have become harsh during the washing process. Most commercially available fabric softeners use tallow-based quaternary actives which deposit onto the garment to provide a soft tactile feel. Unfortunately, the type of quaternary actives that provide softening in the rinse cycle can also leave a yellowish cast on the fabrics. Furthermore, the quaternary can "quench" the fluorescent whitening provided by fluorescent whitening agents (FWA) in the detergent. This tends to reduce the overall whiteness/brightness of the clothing and can leave laundry looking old and dingy. The addition in the fabric softener of a fluorescent whitening agent of the type commercially available for use in laundry products (such as the diamino-stilbene cyanuric chloride derivatives) acts to restore the whiteness/brightness of the garments' appearance that has been lost by the deposition of the softener actives.
Liquid rinse cycle fabric softeners have been commercially available for some time, with consumer usage in excess of 600 million lbs. The major commercial products for many years were aqueous emulsions containing from 3 to 8% by weight of one or more cationic actives. In the last several years, both in the United States and in Europe, higher active level liquid fabric softeners have become an active force in the marketplace. The high active level products (usually greater then 10% active level) provide a convenience to consumers in that they allow for a smaller dosage level to be used to deliver the same softening and antistatic benefits. This permits use of smaller, lighter packages that do the same number of washloads as larger containers of the lower active products. What has not been available to date has been a high active fabric softener that also provides a whitening benefit to the washload. This whitening benefit acts to counteract the yellowing noticed as clothing ages and also restores some of the whitening normally provided by the detergent that is quenched by the deposition of the cationic softener.
While it is desirable to include both softening and whitening agents in a liquid rinse cycle softener, it has proved to be difficult to keep the resultant product viscosity-stable and temperature-stable over the expected lifetime of the product. The stability problems in standard active level (4 to 7%) liquid rinse cycle softeners were overcome as described in Neiditch, et al. U.S. Pat. No. 4,497,718 by use of a non-ionizing base to neutralize the acid form of the fluorescent whitening agent, which permitted the FWA to be solubilized without inclusion of excess electrolyte which acts to reduce the stability of the product. The stability problems become even more difficult in the high active level (&gt;10%) liquid fabric softeners. Softeners containing quaternary actives at high levels become very susceptible to thickening or gelling at low temperature (below 40.degree. F.) storage. The presence of even low levels of electrolyte result in flocculation of the quaternary actives at low temperatures since these can coalesce and gel even though the product is above the freezing point.
The Neiditch, et al. patent (U.S. Pat. No. 4,497,718), mentioned above, describes a liquid fabric softener containing a fluorescent whitening agent complexed with a non-ionizing base of the type used in our invention. Neiditch, et al, teaches the use of these materials in a low active softener system (below 10% active) and does not include the use of Varisoft 222 softener or the like in conjunction with the standard ditallow ammonium chloride active. Burns (U.S. Pat. No. 4,439,335) describes a high active liquid fabric softener that contains both the type of softener in Varisoft 222 and the ditallow ammonium chloride softener. Burns, however, does not include fluorescent whitening agents or non-ionizing base. Burns does not indicate that FWA and non-ionizing base should be used and certainly fails to teach any criticality of the ratio of the two actives when they are combined with a fluorescent whitening agent and non-ionizing base.